Over-voltage protection device for protection of electric equipment



NOV. 25, O. RYDEN OVER-VOLTAGE PROTECTION DEVICE FOR PROTECTION OFELECTRIC EQUIPMENT Filed March 6, 1956 2 h ts-Sheet l I l4=ab /4 ca \AMJEEJEiE LiL 5 a 5 be 5 c/ "V\F r INVQNTOR. OL 01/ RYDEN Nov. 25, 1958 o.RYDEN 2,862,152

OVER-VOLTAGE PROTECTION DEVICE FOR PROTECTION OF ELECTRIC EQUIPMENTFiled March 6, 1956 2 Sheets-Sheet 2 -1 15% 5:66 6 7 EMF INVENTOR. Olov2/ BY W OVER-VGLTAGE PROTECTION DEVICE FOR PRO- TECTION F ELECTRICEQUIPMENT Olov Rydn, llludvika, Sweden, assignor to Allmanna SvenskaElektriska Aktieholaget, Vasteras, Sweden, a Swedish corporation Thepresent invention concerns a modification and improvement of the devicedescribed in patent application Serial No. 449,999. The invention isintended to facilitate the breakdown of a main diverter at an exactvoltage value, the diverter being connected in parallel with someequipment to be protected from over-voltage. This is obtained in asimilar manner to that in the invention mentioned above by connecting inparallel to the equipment to be protected a main diverter consisting ofseveral series connected spark gaps with a voltage divider arrangement,this arrangement distributing the applied voltage across the seriesconnected gaps. An arrangement consisting mainly of an auxiliaryprecision spark gap is connected in parallel with one or more of theseries connected gaps; upon breakdown of the auxiliary gap thisarrangement changes the voltage distribution across the spark gaps andcauses a proceeding breakdown of the gaps. The present inventionconcerns a development of the device described in the patent applicationSerial No. 449,999 and differs from it in two basic respects. In one ofthe modifications the voltage divider is composed of a plurality ofparallel chains, which are alternatively connected to subsequentinter-connecting points of the series connected spark gaps in the maindiverter. The advantage of this arrangement is that when the auxiliarygap is connected in parallel with a part of a voltage divider chain andit is caused to breakdown, the potential of inter-connecting pointsbetween the spark gaps, these being connected to the other voltagedivider chain, remains constant. Another modification of the inventionexists in that the auxiliary gap has been included in an impedancenetwork, this being connected to the main diverter in such a way thatupon breakdown of the auxiliary gap the voltage at the connecting pointwill increase (this is reckoned from the point to which the other poleof the impedance network is connected). The way the voltage is dividedacross the series connected spark gaps, together with the way it ischanged upon the breakdown of the auxiliary gap, initiates theproceeding break down of the series connected spark gaps of the maindiverter.

Both modifications are shown in Figures 1 and 2. Fig. 1 illustrates thedividing up of the voltage divider into two parallel chains, whilst Fig.2 shows the. inclusion of the auxiliary gap in an impedance network forincreasing the voltage at the connecting point.

Figures 3 and 4 show additional modifications of the invention.

The equipment to be protected by the over-voltage protection device is,in Fig. 1, denoted by 1. This equipment is connected to the electricalpower system through its leads 2 and 3. The apparatus 1 protected by themain diverter 4, which is connected in parallel, consists of the seriesconnected spark gaps 4a, 4b, 4c and 4d. Two voltage dividers areconnected in parallel with this main diverter, one of these consists ofthe individual impedances 5a, She and 5d. The value of the impedance 5bcbeing connected in parallel with the series connected 7' States Patent 0spark gaps 4b and 4c, is double the value of the impedance 5a, 5a beingconnected in parallel with the spark gap 4a; or the impedance 5d beingconnected in parallel with the spark gap 40!. The other voltage dividercon-' sists of the impedance elements 14ab being connected in parallelwith the spark gaps 4a and 4b, and of the impedance element 140d whichis connected in parallel with the spark gaps 4c and 4d, the value of thetwo last mentioned impedances being equal. The two parallel voltagedividers divide the voltage across the series connected spark gaps undernormal service conditions in such a way that the voltages across each ofthe spark gaps are equal, i. e. in this case A of the total voltagebetween A and E is found across each of the spark gaps.

The precision spark gap 6 connected in series with an impedance 7 isconnected in parallel with the spark gap 4a and the impedance 5a, i. e.between the points A and B.

In order to appreciate the function of this arrangement one starts fromthe assumption that the entire main diverter with its four seriesconnected spark gaps has to limit the voltage across the apparatus 1 toa value of 100 units. It is assumed that each of these series connectedgaps breaks down at a voltage of to units. When the total voltage acrossthe apparatus 1 is 100 units, a voltage of 25 units only is found acrosseach gap and neither of these will breakdown. The auxiliary precisiongap 6 is assumed to have a breakdown voltage of 25 units and willbreakdown when the voltage across the auxiliary gap 4a amounts to thisvalue. Upon the breakdown of the auxiliary gap the impedance 5a becomesshunted. A new voltage distribution then arises across the seriesconnected gaps. If the voltage across the spark gaps should becontrolled by only one divider chain (the chain comprising impedanceelements She and 5d) the total voltage would then be distributed equallybetween the series connected gaps 4b, 4c and 4d. Each I of these gapswould then have had a voltage of about 33 units and the break down ofany of the series connected gaps could not be reliably expected.

With the aid of the other voltage divider 1411b and 140d the potentialat the interconnecting point of these will be fixed to the value ofunits. As the series spark gap 4a is practically short circuited by theauxiliary spark gap 6, a voltage of 50 units is found across the otherspark gap 412. This gap will then distinctly breakdown and a new voltagedistribution is obtained. If only one voltage divider chain had beenemployed, the voltage across the spark gap 40 would have been 50 units.When two chains are provided, the voltage divider consisting of elementsShe and 5d distributes the voltage in the ratio 2 to 1. The spark gap 4bis practically short circuited, and two thirds of the total voltage, i.e. about 67 units, will be found across the series gap 40. This gap thenbreaks down with the result that the total voltage of units is foundacross the last spark gap 4d. As the series impedance '7 is highcompared with the internal resistance of the arc in the series gaps 4b,4c and 4d the voltage across the gap 4a is increased to such a valuethat this gap is caused to break down and let the current pass. Theauxiliary gap 6 is hereby unloaded and extinguished.

All the series connected spark gaps in the main diverter have now brokendown and protect the apparatus 1 from over-current and limit the voltageacross the apparatus 1 to an acceptable value. It should be clear thatby substituting two parallel voltage divider chains for the one usedpreviously the voltage of 33 units across the gap 4b has been increasedto 50 units, similarly the voltage across gap 4c has been increased from50 to 67 units.

The voltage increase becomes more pronounced the higher the number ofseries spark gaps in the diverter. With an adequate number of gaps thevoltage increase across the first series connected gaps would be 100%.

Considering this modification of the main invention, there is also thepossibility of connecting the auxiliary gap 6 with its impedance 7 toother points of the voltage divider 5, than to the one denoted B in thefigures. In this way a still higher voltage increase can be obtainedacross the first igniting series connected gaps. Furthermore, thevoltage dividers and 14 can be resistive, inductive, capacitive or becomposed of a combination of these elements. Voltage dividers are,however, preferably made up of a chain of resistive elements havingcapacitive elements connected in parallel. The circuit diagram for thisarrangement is given in Fig. 4. The resistive elements then provide fora correct voltage distribution at comparatively low frequencies, whilstthe capacitive part determines the voltage distribution for surges witha steep front. The series impedance 7 is suitably designed as anon-linear resistance in order to facilitate the unloading of theauxiliary gap 6, when the series gap 4a has ignited.

The other modification is illustrated in Fig. 2. 'As in Fig. 1, thisfigure shows the equipment 1 being connected to the electrical powersystem over the leads 2 and 3. The diverter 4 consists of the seriesconnected gaps 4a, 4b, 4c and 40'. 'One voltage divider chain 5 isemployed consisting of the elements 5a, 5b, 5c and 5d, these being ofsubstantially the same value. The auxiliary precision spark gap 6 is, inthis case, included in an impedance network consisting of two branches,one branch consisting of the impedance and the capacitance 17, the otherbranch consisting of the impedance 16 and the capacitance 18. Theauxiliary precision spark gap 6 constitutes a diagonal in this network.The impedance network is then connected to point X in the voltagedivider 5 via an impedance 19 and it is also connected directly to pointC of the main diverter 4. The other terminal of this impedance networkis connected to one of the end terminals of the voltage divider 5. Theimpedances l5 and 16 are preferably designed as resistances with lowohmic values. The impedance 19 is as a rule, designed as a resistance oran inductance of low value.

In order to appreciate the function of this arrangement it should beassumed that the entire diverter with its four series connected sparkgaps has to limit the voltage across the apparatus 1 to a value of ahundred units. It is furthermore assumed that each of these seriesconnected gaps break down at a voltage of to units. When the totalvoltage across the apparatus 1 is a hundred units, a voltage of 25 unitswould be found across each of the spark gaps if no impedance networkwith an auxiliary gap had been employed, consequently none of thesewould break down. The precision auxiliary gap 6 is here assumed to havea breakdown voltage of units. If now a total voltage of a hundred unitsappears across the apparatus 1 half of this value, i. e. 50 units, isfound between terminals H and X of the voltage divider. The capacitances17 and 18 are each charged with this voltage. Upon the break down of theauxiliary gap 6 these two capacitances will be connected in series, theimpedance network thereby injecting a voltage of 100 units at point C inrelation to point A. If the voltage divider 5 is considered to be stiffcompared with the impedance network, i. e. have a relatively lowimpedance value in relation to that of the impedance network, thefollowing voltage distribution across the series connected spark gaps isobtained: plus 25 units across the gap 4a (25 units (B)0 units (A)=25units), plus 75 units across the gap 412 (100 units (C)25 units (B):75units) minus 25 units across the gap dc (75 units (D)1t)0 units (C): 25units) and plus 25 units across the gap 4d (100 units (E)75 units (D):25units). On account of the high voltage, the spark gap 4b then breaksdown, and a new voltage distribution is obtained as follows:

Presuming again that the voltage divider dominates,

from the apparatus 1. The conditions will be even more favourable whenwe presume that the voltage distribution after the first ignition isdetermined by both the voltage divider 5 and the impedance network incooperation, i. e. when the effect of the network cannot be negligiblein relation to the voltage divider. In this case the voltage across theseries connected gaps will be higher and an even more distinct breakdown can be expected. In the arrangement illustrated in Fig. 2, theimpedance elements in the voltage divider 5 may be composed of acombination of impedance elements, preferably resistances andcapacitances. The invention is not restricted to the way the impedancenetwork is connected as shown in the illustrations and the impedancenetwork may be connected to other points than to C and X. The connectionof the impedance network to the main gaps may also be made via anadditional auxiliary spark gap. The impedance network may furthermore bedesigned for more than two branches, hereby more than two capacitors canbe connected in series upon the ignition of more than one auxiliary gapand the voltage at the injection point will then be even higher.Arrangements may also be made for dividing up the voltage divider 5 inFig. 2, into several chains connected in parallel, as in Fig. 1.

The arrangements described may be improved by connecting the voltagedividers to the main diverter, this main diverter consisting of aplurality of series connected spark gaps, through coupling impedances asillustrated in Fig. 3. The advantage of this arrangement is that thevoltage distribution will be influenced to a smaller degree by thebreakdown process in the main gap chain than would otherwise beencountered. The coupling impedances consist preferably of resistances20, capacitances 21 or both combined, and are connected be tween thevoltage dividers and the connecting terminals of the series connectedspark gaps. The same reference numbers have been used in Fig. 3 as inFig. l. The loose coupling principle, i. e. the connecting of the seriesconnected spark gaps to the impedance elements of the voltage dividerthrough coupling impedances, may of course also be applied to anarrangement being a combination of the devices illustrated in Figs. 1and 2.

I claim as my invention:

1. A diverter to protect electrical equipment, comprising a plurality ofindividual spark gaps connected in series over joining terminals, meansbeing provided for connecting said chain of spark gaps across saidelectrical equipment and forming a main diverter across said equipment,a plurality of impedance elements being series connected over joiningterminals to form a plurality of impedance chains conductive for directcurrent, means being provided for connecting said chains of impedanceelements in parallel with said main diverter, said impedance chainsforming a plurality of voltage dividers, means being provided forconnecting said joining terminals of said voltage dividers to alternatejoining terminals of said chain of spark gaps, a precision sparkover gapand a non-linear type resistor series connected; means being providedfor connecting said precision spark gap and nonlinear resistor inparallel with at least one impedance element in one of said voltagedividers.

2. A diverter to protect electrical equipment, comprising a plurality ofindividual spark gaps connected in series over joining terminals, meansbeing provided for connecting said chain of spark gaps across saidelectrical equipment, forming a main diverter across said equipment, aplurality of impedance elements being series connected over joiningterminals forming two impedance chains conductive for direct current,means being provided for connecting said chains of impedance elements inparallel with said main diverter, said impedance chains forming twovoltage dividers, means being provided for connecting joining terminalsof said voltage dividers alternately to every joining terminal of saidchain of spark gaps, a precision spark over gap and a non-linear typeresistor series connected, means being provided for connecting saidprecision spark gap and valve-type resistor in parallel with at leastone impedance in one of said voltage dividers.

3. A diverter to protect electrical equipment, comprising a plurality ofindividual spark gaps connected in series over joining terminals, meansbeing provided for connecting said chain of spark gaps across saidelectrical equipment, forming a main diverter across said equipment, aplurality of impedance elements, each of them being composed ofresistive and capacitive components in parallel connection, theimpedance elements being series connected over joining terminals to forma plurality of impedance chains, means being provided for connectingsaid chains of impedance elements in parallel with said main diverter,said impedance chains forming a plurality of voltage dividers, meansbeing provided for connecting said joining terminals of said voltagedividers to alternate joining terminals of said chain of spark gaps, aprecision spark-over gap and a non-linear type resistor seriesconnected, means being provided for connecting said precision spark gapand valve-type resistor in parallel with at least one impedance in oneof said voltage dividers.

4. A diverter to protect electrical equipment, comprising a plurality ofindividual spark gaps connected in series over joining terminals; meansbeing provided for connecting said chain of spark gaps across saidelectrical equipment, forming a main diverter across said equipment, aplurality of impedance elements, said impedanceelements forming avoltage divider conductive for direct current across said main diverter,impedances comprising capacitive components forming an impedancenetwork, means being provided for connecting said impedance network inparallel with at least one of said individual spark gaps, at least oneprecision spark over gap connected to said impedance network in such away that otherwise separated terminals of said capacitive components ofthe network are connected together upon breakdown of said precisionspark over gap.

5. A diverter to protect electrical equipment, comprising a plurality ofindividual spark gaps connected in series over joining terminals, meansbeing provided for connecting said chain of spark gaps across saidelectrical equipment, forming a main diverter across said equipment, aplurality of impedance elements forming a voltage divider conductive fordirect current across said main diverter, a plurality of impedanceelements forming at least one four-armed bridge network, capacitances tobe included in at least two opposite arms of said bridge, said networkshunting at least one of: said individual spark gaps at least duringover-voltage conditions, and a precision spark-over gap connected as adiagonal to said bridge, connecting said capacitances in opposite armsin series upon breakdown of the precision spark-over gap.

6. A diverter to protect electrical equipment, comprising a plurality ofindividual spark gaps connected in series over joining terminals, meansbeing provided for connecting said chain of spark gaps across saidelectrical equipment forming a main diverter across said equipment, aplurality of impedance elements being series connected over joiningterminals to form a plurality of impedance chains, means being providedfor connecting said chains of impedance elements in parallel with saidmain diverter, said impedance chains forming a plurality of voltagedividers, a plurality of coupling impedances, means being provided forconnecting at least one of said chains of voltage dividers to alternatejoining terminals of said chain of spark gaps over said couplingimpedances and for connecting the remaining voltage dividers to theother alternate joining terminals of said chain of spark gaps, aprecision spark-over gap and a non-linear type resistor seriesconnected; means being provided for connecting said precision spark gapand non-linear resistor in parallel with at least one impedance elementin one of said voltage dividers.

Great Britain Nov. 18, 1920 France June 21, 1951

